Define what happens with @page { counter-increment: none; }

"Maybe we want the page counter to behave the same as the list-item counter in the latest Lists 3 editor’s draft: the implicit increment only happens if the counter-increment is not otherwise specified. This can be implemented with an 'auto' initial value, for counter-increment but that value should serialize to 'none' (the real initial value in CSS 2.1) when authors request the computed value."

We can also just have 'none' behave as the 'auto' value; to turn off incrementing, you have to explicitly specify 'counter-increment: page 0'.